1. Field of the Invention
The present invention relates to a biosensor which comprises a substrate, an insulating layer, source and drain electrodes formed on the insulating layer, a middle-discontinuous channel provided between the source and drain electrodes, and a detection area covering the middle-discontinuous channel on which a target material to be detected is fixed, a method of producing the same, and a method of detecting a biomaterial using the biosensor. More particularly, the present invention relates to a biosensor detecting a target biomaterial, wherein a receptor is fixed on a detection area, the receptor is selectively coupled with a target biomaterial, while a contact resistance is changed by the selective coupling of the receptor with the target biomaterial, and thus the amount of an electric current flowing from a source electrode to a drain electrode is changed, when using a carbon nanotube-electric field effect transistor to detect a biomaterial, a method of producing the same, and a method of detecting a target biomaterial using the biosensor.
2. Description of Related Art
A biosensor may refer to “a system that converts information acquired from a target to be measured into a recognizable signal such as color, fluorescent, and electrical signals by using a biological element or copying a biological system.” A biosensor may be constructed in various forms in accordance with a target material to be measured, a biological element fixed on the sensor, and the kind of a signal converter. For signal conversion, there have been used various physical and chemical techniques such as electrochemical, thermal, optical and mechanical techniques.
There have been various biosensors according to a target material to be measured, a biological element fixed on the sensor, and the kind of a signal converter. The first biosensor is known as a Glucose sensor made by using a dialysis membrane by Clark for measuring glucose in 1962. In the early stage, most of biosensors are made by fixing an enzyme on a signal converting device. However, sensors made using a monoclonal antibody, an antibody-enzyme conjugate, etc. have recently been developed with rapid development of molecular biology. Also, researches and development of chip sensors such as a DNA chip, a protein chip or the like for processing massive genetic information at super-high speed have become active, and a lot of efforts have been concentrated on the development of high-technology sensors in which molecular biotechnology, nanotechnology and information and communication technology are fused.
A biochip refers to a chip formed by fixing bio-molecules such as DNA, protein, etc. on a small substrate made of glass, silicon, nylon or a like. A DNA-fixed biochip is called as a DNA chip, and a protein-fixed biochip is called as a protein chip. Also a biochip is broadly classified into a microarray chip and a microfluidics chip. A microarray chip is a biochip where thousands or scores of thousands of DNAs, proteins, etc. are attached at regular intervals and process a target material to be analyzed on the chip, and analyze the bonding pattern. A DNA chip, a protein chip or the like are the representative microarray chip. A microfluidics chip is also called as a lab-on-a-chip, which can analyze a reacting pattern by injecting a very small amount of target material to be analyzed and observing various bio-molecular probes or sensors fixed on the chip. A DNA chip is classified into an oligonucleotide chip, a cDNA chip, a PNA chip, etc. according to the kind of probes to be fixed. A oligonucleotide chip is a new technique for probing genetic diversity on a large scale, in which a large number of synthetic oligonucleotides are attached to a certain correct position of a very small space of a support and hybridizes with a very small amount of target base sequence so that many genes can be searched at the same time. Such an oligonucleotide chip is expected to make a major contribution to a drug-resistant diagnosis, mutant search, single nucleotide polymorphism (SNP), a disease diagnosis or genotyping.
A biosensor can be classified as roughly six application fields as follows.
1. Clinical diagnosis and medical field: This field takes up about 90% of the overall biosensor market. It is mostly occupied by a glucose sensor for sensing blood sugar, but a market share of the biosensors capable of sensing various biomaterials such as lactic acid, cholesterol, urea, etc. is expected to become high since a demand for point-of-care testing (POCT) rapidly increases.
2. Environment: A biosensor is used for detecting an environment-related substance such as an endocrine disruptor, a biochemical oxygen demand (BOD) of waste water, a heavy metal, an agricultural chemical, etc. Researches on a sensor that has selectivity to various endocrine disruptors such as dioxin and is capable of sensing low concentration have been in progress from various angles.
3. Food: A biosensor is applied to food safety inspection, for example, for use in detection of hazardous substances such as residual agricultural chemicals, antibiotics, pathogens, a heavy metal, etc.
4. Military: A biosensor is used for sensing a biochemical weapon for mass destruction, such as sarin, anthrax, etc. To cope with a biological weapon, a biosensor requires quick sensing time and miniaturization to be used in a field.
5. Industry: A biosensor is used for controlling a growing condition of a microorganism in a fermentation process, or for monitoring specific chemical substances generated in chemistry/petro-chemistry, pharmaceuticals, and food processing, etc.
6. Researches: A biosensor is used for analyzing the speed of bonding between biomaterials, and sensing the behavior of a single molecule.
An electric field effect transistor is a device which is used to convert a voltage signal inputting to a gate electrode into an electric current signal to outputting from a source electrode or a drain electrode. An electric field effect refers to a phenomenon that when an electric field is applied to the semiconductor, a conductive channel is formed so that electricity can flow as carriers (free electrons or holes) within a semiconductor move depending on the applied electric field in such a manner that (−) carriers, i.e., electrons are collected in a (+) side, and (+) carriers, i.e., holes are collected in a (−) side.
Where voltage is applied between the source and drain electrodes, charged particles existing in a channel move along a direction of the electric field between the source electrode and the drain electrode, and then voltage is outputted as a current signal from the source electrode or the drain electrode. At this time, the intensity of the outputted electric signal is proportional to the density of the charged particles. Where voltage is applied to a gate electrode installed on the top, laterals, bottom, etc. of a channel through an insulator, the density of the charged particles existing in the channel is changed. Upon this fact, by changing gate voltage, an electric current signal is changed.
A carbon nanotube has electric conductivity as excellent as copper, thermal conductivity as excellent as diamond, strength a hundred times higher than a steel with a ⅙ weight, and strain resistant to breaking. A carbon nanotube, discovered by Japanese Dr. Iijima in 1991, shows several unique quantum mechanical phenomena due to a quasi-one-dimensional quantum structure; and has characteristics such as a very small diameter of several to several tens of nanometers (nm), a large length to diameter ratio, and a hollow structure. Due to a very unique one-dimensional carbon structure, the carbon nanotube has excellent mechanical, thermal, electrical properties, and is evaluated as a new material for the next-generation. Due to lots of merits thereof, particularly, the excellent mechanical properties and the high electric and thermal conductivities, a variety of applications of the carbon nanotube to an electric field effect transistor, a flat panel display device, an electronic device, etc. have been researched throughout industry. Further, an attempt to apply the carbon nanotube to a biosensor has increased.
For example, the application to a transistor device has been researched as follows. In 1998, researchers of Delft University of Technology in the Netherlands materialized the carbon nanotube as a transistor that operates at a room temperature (Sander J. Tans et al., Nature, 1998, 393, 49). The experimental result shows that an electronic device based on the carbon nanotube which has excellent properties in the physical and electrical aspects can operate a hundred times faster, can be more highly integrated, and can have lower power-loss than a conventional electronic device based on silicon. This is the first instance that shows applicability in an electronic device based on a carbon nanotube in the future.
Thereafter, various applications of a nano-devices based on the carbon nanotube has been presented by many research institutions all over the world through a lot of papers, patents, etc. up to now (as of 2009). In 2009, group researchers of Harvard University in the U.S.A. introduced an experimental result of a highly-sensitive measurement of change in a surface charge of a biomaterial, using a carbon nanotube as a channel in a biosensor based on an electric field effect transistor (Charles M. Liber et al., Science, 2001, 293, 1289). Since then, developed technology made it possible to measure a large change in the surface charge through enzyme reaction, and then to measure a minute change in the surface charge of protein-protein bonding. Recently, the technology has reached measuring a change in a surface field due to approach of protein. In 2005, researchers of Chungnam National University in Korea and Korea Research Institute of Chemical Technology introduced a concept of the biosensor using the carbon nanotube-electric field effect transistor (CNT-FET). This is based on the feature that electric conductivity through a carbon nanotube decreases while the negative charges of an aptamer disappears when a DNA aptamer is attached on the surface of a carbon nanotube using CDA-Tween 20, as a linker, which materializes a high-performance CNT-FET biosensor capable of measuring a certain target molecule at a level of 10 nM (Hye-Mi So, et al., J AM. Chem. Soc., 2005, 34, 11906). By ongoing researches, it is announced that the sensitivity enhances as a bonding distance between the surface of the carbon nanotube and a biomaterial to be detected becomes close. By the research, the industrial applicability of the technology has increased by succeeding IgE detection of 1.8 nM using a CNT-FET sensor (Kenzo Maehashi, et al., Anal. Chem., 2007, 79, 782).
Korean Patent First Publication No. 2007-53545 relates to a technique in which the conductivity is increased by the carbon nanotube attached to a target molecule when the target molecule hybridizes with a probe, and thus it is possible to easily detect the hybridization of the target molecule, which discloses a biochip including a top electrode, a bottom electrode and an insulating layer interposed between the top and bottom electrodes.
Korean Patent Registration No. 10-455284 relates to a technique in which respective receptors are arbitrarily fixed to a certain position on a chip by applying electric charges having opposed polarity to net charges of various receptors to be bonded with a target bio-molecule to a carbon nanotube after growing the carbon nanotube having a nanometer diameter on a non-conductive substrate, and thus high-integration or array with a desired pattern is possible at a nano (10−9) level rather than a conventional array technology of a micro (10−6) level, which discloses a nano-array type bio-molecule detecting sensor that includes a substrate and a plurality of carbon nanotubes arrayed on the substrate, in which the receptor to be bonded with the target bio-molecule is selectively attached onto the carbon nanotube at a desired position by applying an electric field to the carbon nanotube.
In addition, Korean Patent First Publication No. 2007-22165 discloses a sensor for detecting a detection target material through a field effect transistor which comprises a substrate, source and drain electrodes and a channel for a path of electric current between the source and drain electrodes, in which the electric field effect transistor includes an interaction sensing gate for fixing a certain material selectively interacting with the detection target material, and a gate to which voltage is applied to detect this interaction by a characteristic change of the electric field effect transistor.
However, despite such efforts of many researches, a research result for application of the biosensor using the carbon nanotube has not been disclosed yet with respect to the detection material having a low concentration of 1 nM or less.